I cut each pad the same shape (what I sketched in chalk, basically) which is 40" wide at the shoulder and the whole 70" long. I made 1 in 3/8" minicel, and one in 1/4" minicel, figuring I could layer them for extreme weather, and use either for warmer temps. I have not yet had a chance to try them (sob!) but will give them a field test on April 15th.
I tried to use a hotknife for the cutting, but it was ridiculously too slow, so I switched to shears.
Then I got ambitious and made a custom 1.7 nylon bag for the pads, since they're so wide they roll up to be longer than my backpack. I added a set of grograin loops for attachment, and a set of loops for my fishing pole (conveniently, almost 40" long). Foam came from these guys: http://www.foambymail.com/Minicel.html
Many pics included, hope some of them help.
I anticipate that I cut them too wide, although they seem to have just about the right amount of wrap around my shoulders to prevent cold-shoulder-syndrome, and I figure that later I may want to cut darts in where it bends, to permit better flexing.
I hope this helped! If not, please ask, I'll do my best to offer more info.